Furfural and related compounds, such as hydroxymethylfurfural (HMF), are useful precursors and starting materials for industrial chemicals for use as pharmaceuticals, herbicides, stabilizers, and polymers. The current furfural manufacturing process utilizes biomass such as corn cob and sugar cane bagasse as a raw material feed stock for obtaining xylose or hemicellulose.
The hemicellulose is hydrolyzed under acidic conditions to its monomer sugars, such as glucose, fructose, xylose, mannose, galactose, rhamnose, and arabinose. Xylose, which is a pentose (i.e., a “C5 sugar”) is the sugar present in the largest amount. In a similar aqueous acidic environment, the C5 sugars are subsequently dehydrated and cyclized to furfural.
A major difficulty with known methods for dehydration of sugars is the formation of undesirable resinous material that not only leads to yield loss but also leads to fouling of exposed reactor surface and negatively impacts heat transfer characteristics. Further, the use of solid acid catalyst could also lead to coking issues.
A review by R. Karinen et al. (ChemSusChem 4 (2011), pp. 1002-1016) includes several commonly used methods of producing furfural generally as described above. All of those methods involve use of a soluble inorganic acid catalyst, such as sulfuric, phosphoric, or hydrochloric acid. These acids are difficult to separate from the reaction medium or product stream. Low yields can result from formation of undesirable byproducts. Further, their use can require increased capital costs because of associated corrosion and environmental emission issues.
There remains a need for a process to produce furfural and related compounds from sugars at both high yield and high conversion.